1. Field of the Invention
This invention relates to multi-stage rocket motor assemblies (e.g., for missiles) having at least one of its stages capable of being jettisoned in flight, and especially to multi-stage rocket motors having a jettisonable flight motor stage and launch motor stage.
2. Description of the Related Art
Dual-stage rocket motor assemblies are well known in the industry and have found various practical applications, most commonly in connection with their use as the propulsive impulse systems of guided and unguided missiles. As understood in the art and referred to herein, a multi-stage rocket motor assembly includes at least the following two stages. First, a launch motor subassembly provides thrust for lift-off or, in the case of a canister-launched missile, ejection from the canister, and optionally for initial flight. Alternatively, in the case of a boost motor subassembly, the propulsive force for the initial flight of an aircraft-launch rocket motor assembly can be provided by the boost motor subassembly. Second, a main motor subassembly is actuated after depletion of the launch motor subassembly propellant and supplies at least a portion of the flight propulsion to the rocket motor assembly. In the case of a boost/sustain motor, the main motor commonly functions as the sustain stage.
Multi-stage rocket motor assemblies are well known and have been accepted for various applications. One example of an application for dual-stage rocket motors is the use of such rocket motors in canister-launched missiles. The launch motor subassembly provides the initial impulse for expelling the missile from the canister to a sufficient distance to permit ignition of the main motor subassembly without danger of injury to the operator and/or launcher. Additionally, multi-stage rocket motor assemblies have also been used for anti-aircraft missiles. The efficiency with which an anti-aircraft missile is able to intercept an aircraft can be increased by imparting an additional impulse from the main motor subassembly immediately prior to final targeting and intercepting of the intended target. The additional impulse increases the maneuverability of the missile and reduces the period available to the intended target for making last, second evasive adjustments. Another example of a situation in which dual-stage rocket motors have been used is where a boost/sustain function is desired, such as for travelling over long flight distances and for aircraft-launched rocket motor assemblies. In a boost/sustain system, the launch motor subassembly contains a boost propellant designed to burn at a rate suitable for attaining initial flight and acceleration of the rocket motor assembly, whereas the propellant of the main motor subassembly is designed to burn at a slower rate for longer periods of time.
In each of the above-discussed applications, certain performance advantages are obtained by designing the multi-stage rocket motor assembly to permit detachment of the launch (or boost) motor subassembly from the main motor and jettisoning of the spent launch motor subassembly after expenditure of the launch motor subassembly propellant. The firing of the main motor subassembly is synchronized with the jettisoning of the launch motor subassembly to achieve a designed flight profile.
It is an object of this invention to provide a propulsive impulse system of a dual-stage rocket motor that experiences a reduced weight penalty during the flight stage of the rocket motor than known rocket motors so that the performance of the propulsive impulse system is improved in terms of flight duration and/or flight velocity.
In accordance with the principles of this invention, these and other objects are attained by the provision of a rocket motor assembly comprising at least one primary motor subassembly, such as a main or sustain motor subassembly, and at least one launch (or boost) motor subassembly. The primary motor subassembly comprises at least one flight igniter, a main motor case structure housing at least one main combustion chamber loaded with at least one main propellant which is ignitable by the flight igniter, and a nozzle subassembly with a throat portion constructed and arranged to permit combustion products produced by combustion of the main propellant to be received from the main combustion chamber and passed through the throat portion. The launch (or boost) motor subassembly comprises at least one launch igniter and a launch motor case structure, which houses at least one launch combustion chamber loaded with at least one propellant grain which is ignitable by the launch igniter.
The launch motor subassembly is jettisonable, meaning that it is capable of being detached from at least the nozzle subassembly while the rocket motor assembly is in flight to permit the launch motor subassembly to be: separated and ejected from the main motor case structure and the nozzle subassembly substantially simultaneously with or after ignition of the main propellant. According to this invention, the flight igniter is integrated with the launch motor subassembly. As referred to herein, integrated in this context means that the flight igniter is jettisoned essentially in unison with the launch motor subassembly by detachment of the launch motor subassembly from at least the main motor nozzle subassembly.
By jettisoning the flight igniter essentially simultaneously with the launch motor subassembly, the weight of the main motor subassembly is lessened during operation of the flight motor stage, i.e., the flight igniter is removed as a weight penalty. As a result, in the case of an anti-aircraft, anti-tank, and anti-personnel missiles and the like, acceleration and distance traveled during the intercept stage can be increased, thereby improving performance. Likewise, in the case of a boost/sustain missile, because the weight penalty has been decreased during the sustain stage by jettisoning the boost stage, the acceleration and distance, traveled by the missile are increased.
These and other objects, aspects and advantages of the invention will be apparent to those skilled in the art upon reading the specification and appended claims which, when read in conjunction with the accompanying drawings, explain the principles of this invention.